Os01g0205700

OsGSK1 (Oryza sativa glycogen synthase kinase3-like gene 1), a member of the plant GSK3/SHAGGY-like protein kinase genes, with enhanced tolerance to various abiotic stresses and an orthologue of the Arabidopsis brassinosteroid insensitive 2 (BIN2), AtSK21.

Annotated Information

Function

OsGSK1 had a highly conserved kinase domain, a variable region in the N- and C-terminals, and a TREE domain. That TREE domain is highly conserved among GSKs and likely plays a critical role in the functioning of GSKs. It is involved in floral development because of its high expression in the developing panicles and functions as a negative regulator in the general abiotic-stress response in rice. OsGSK1 showed enhanced tolerance to several abiotic stresses including high temperature..

GO assignment(s): GO:0004672, GO:0005524, GO:0006468

Mutation

Figure 1. Salt and drought tolerance tests of OsGSK1 KO mutant.(from reference ).

Table 1. Wilting ratios for OsGSK1 knockout and non-transgenic plants after stress treatments.(from reference ).

• To examine the role of OsGSK1 in the abiotic-stress response, Serry Koh et al. analyzed the tolerance of OsGSK1 KO

mutants by measuring chlorophyll fluorescence and the wilting ratio after 8-day-old seedlings were treated with drought, cold, salt, or heat (Fig 1 and Table 1).

• Compared with our NT plants, the wilting ratios for KO mutants wereabout 20% lower after cold stress (4) and as much as 26% lower after heat (45) stress (Table 1).It is a transgenic rice with increased heat tolerance.
• The wilting ratios for KO were lower each 13% and 36% than NT plants by 100 mM and 250 mM NaCl treatment, respectively(Fig. 1A–C)For our drought-tolerance test, leaves from hydroponically grown 8-day-old KO and NT seedlings were air-dried on filter paper. Under normal growing conditions, the ratio of Fv to Fm was 0.82 ± 0.01 for both KO and NT plants(Fig. 1D).
• However, changes in Fv/Fm values varied between these genotypes, showing a slower decline in the KO mutants. After 6 h of drought treatment, the KO ratio was reduced to 0.47 ± 0.15, which was >2-fold higher than that of NT plants. These data indicated that the OsGSK1 KO mutant had enhanced tolerance to drought stress.

Expression

Figure 2.Histochemical localization of GUS activity and morphological alteration of OsGSK1 KO mutant.(from reference ).

• OsGSK1 transcript was detected, at varying levels, in all these tissues or organs except for mature leaves. Expression was highest in the young panicles, with slightly less detection in the calli, implying possible physiological role of OsGSK1 in developing tissues.
• Northern blot analysis: Following cold treatment, transcript levels reached a maximum at 3 h, then decreased. Under salt stress, transcripts slightly increased. Drought stress caused a gradual decrease in transcript levels over 24 h. Under ABA treatment, expression was not significantly different from that detected in our control. These results indicate that OsGSK1 transcript accumulations are regulated differently by environmental stresses.
• GUS expression and morphological alteration of OsGSK1 KO mutant:
  • GUS activity was strong in the root tips and root hairs but was more weakly detected in the shoots (Fig. 2A).
  • In the latter, activity was localized to the lamina joint in the collar region. GUS activity also was detected in the vascular bundles of the coleoptile (Fig. 2E).
  • In contrast to our Os-GSK1 KO, non-transgenic (NT) plants exhibited no GUS activity (data not shown). At the flowering stage, activity was highly detected in the entire young panicle (Fig. 2D).
  • In the spikelet, GUS activity was found in the awn and vascular bundles of the palea and lemma (Fig. 2B).
  • Whereas activity was strong in the stigma and rachilla, it was barely detected in the anther (Fig. 2C).

Evolution

Figure 3. Phylogenetic tree of OsGSK1 with other plant GSKs including BIN2-homologues(from reference ).

• OsGSK1 was classified into Subgroup II with AtSK21, AtSK22, AtSK23, and OsSKetha (Fig. 3). Among those members, OsGSK1 had the highest similarity with AtSK21, which is known as a negative regulator of brass inosteroid signaling, BIN2.
• The Arabidopsis genome contains 10 GSK3/SHAGGY-like genes, and Brassinosteroid Insensitive 2(BIN2) encoding AtSK21shares the highest sequence similarity to OsGSK1.

Knowledge Extension

Phylogenetic study of plant GSK3/SHAGGY-like kinase has revealed nine GSK3/SHAGGY-like kinase homologues in rice, including OsGSK1.

• The GSK3/SHAGGY-like kinases are multi-functional non-receptor Ser-Thr (S/T) kinases. Arabidopsis dwf12 mutants, which are allelic with bin2 and ucu1 mutants, are all mis-sense mutations in the TREE domain that alter kinase activity .

In higher plants, the GSK3/SHAGGY-like kinases are a small family of Ser/Thr protein kinases that function in various developmental processes, e.g., hormone/stress-signaling and floral development . However, because rice has at least four BIN2-homologues in Group II and because their functions may overlap, further studies, such as kinase assays and crosses with the OsBRI1 mutant, are needed to verify OsGSK1 as a rice BIN2 (OsBIN2). OsGSK1 has the highest amino acid sequence homology with Arabidopsis BIN2/AtSK21, a negative regulator of BR-signaling .BRs are steroidal hormones ubiquitously distributed in plant species. BRs play an important role in various cellular responses, e.g., stem elongation, pollen tube growth, xylem differentiation, leaf epinasty, and root inhibition.

Labs working on this gene

• Department of Life Science, Sogang University, Seoul 121-742, Korea
• Department of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea
• National Research Laboratory of Plant Functional Genomics, Department of Life Science, Pohang University of Science and Technology, Pohang 790-784, Korea
• National key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research (Wuhan),Huazhong Agricultural University,Wuhan 430070,China